1. Technical Field
The present invention relates to a spindle device for a machine tool, provided with: a spindle which is arranged rotatably about an axis and to which a tool is attached; and a drive motor for rotating the spindle about the axis.
2. Description of the Related Art
In a spindle device for a machine tool, such as a machining center, progress has been conventionally made in achieving a higher speed of a spindle rotation. The reason for this is to implement a higher speed machining to shorten a machining time, thereby achieving effective machining. On the other hand, depending on a quality of material for a workpiece, which is an object to be machined, the high-speed cutting is not possible, and thus, there may be a need of rotating the spindle at a low speed to carry out the machining. However, a spindle device corresponding to the high-speed cutting has small output at the time of the low-speed rotation, and thus, low-speed cutting cannot be carried out. As a result, there is a limit to a single machine tool carrying out all types of machining works.
On the other hand, conventionally, for a spindle device that has large output even at the time of the low-speed rotation, that which is disclosed in JP-A-H11-99433 (hereinafter, referred to as Patent Document 1), for example, is proposed, but in Patent Document 1, instead of a tool, a workpiece is attached to the spindle. The spindle device is provided with: a housing; a first rotation axis and a second rotation axis disposed in a manner to be kept apart by a distance in an axial direction within the housing; a spindle connected to one end side of the second rotation axis; a first drive motor and a second drive motor for causing each rotation axis to rotate about its axis; and a clutch mechanism disposed between the first rotation axis and the second rotation axis.
The first drive motor includes a first rotor arranged on an outer circumferential surface of the first rotation axis and a first stator arranged on an inner circumferential surface of the housing. For the first drive motor, that which has large output even at the time of the low-speed rotation is used. On the other hand, the second drive motor includes a second rotor arranged on an outer circumferential surface of the second rotation axis and a second stator arranged on an inner circumferential surface of the housing. For the second drive motor, that which is adapted for the high-speed rotation is used. The clutch mechanism carries out a connecting operation for connecting the one end side of the first rotation axis and the other end side of the second rotation axis, and a releasing operation for releasing the connection between the one end side of the first rotation axis and the other end side of the second rotation axis.
In this spindle device, at the time of the high-speed rotation of the spindle, the second drive motor is driven in a state that the connection between the first rotation axis and the second rotation axis is released by the clutch mechanism; and at the time of the low-speed rotation of the spindle, the first drive motor is driven in a state that the connection between the first rotation axis and the second rotation axis is released by the clutch mechanism.
In the spindle device to which the tool is attached, a clamping device for clamping/unclamping the attached tool is generally placed. This clamping device draws the tool into an attaching hole of the spindle for clamping. The clamping device is configured by: a drawing member, disposed movably in an axial direction within the attaching hole of the spindle, for drawing the tool into the attaching hole; and a drive mechanism, placed on the rear end side of the spindle, for clamping and unclamping the tool by the drawing member.
Therefore, it is not possible to directly apply the spindle device disclosed in the Patent Document 1 so configured that the spindle, the first rotation axis, the clutch mechanism, and the second rotation axis are disposed in a straight line in the axial direction of the spindle, to the spindle device in which the above-described clamping device is arranged. Further, when the spindle, the first rotation axis, the clutch mechanism, and the second rotation axis are merely disposed in the axial direction of the spindle, a length in the spindle axial direction in the spindle device is elongated, thereby resulting in a problem in that a device configuration becomes large.
In view of the above-described circumstances, the present invention has been achieved, and an object thereof is to provide a spindle device for a machine tool capable of being compatible with both high-speed cutting and low-speed cutting while remaining compact in size.